This non-provisional application claims priority under 35 U.S.C. xc2xa7119(a) to Japanese Patent Application No. Hei-10-221684, filed Aug. 5, 1998, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a method of preventing data destruction in a multiplex communication system. The invention acts to prevent surviving transmission data from being destroyed whose transmission was stopped due to the delay in collision detection in a network communication based on CSMA/CD (Carrier Sense Multiple Access with Collision Detect).
2. Background Art
In network communication based on CSMA/CD, two or more communication apparatuses connected to the network simultaneously start sending transmission data, these communication apparatus keep sending the transmission data while the same transmission data is flowing over the network, then, when they start indicating a mismatch in the transmission data, those communication apparatus which are prioritized over others in the transmission data survive, and the communication apparatus having the highest priority ultimately survives to continue sending the transmission data.
In the above-mentioned communication scheme, if the other communication apparatus are not outputting transmission data over the network, the communication apparatus in question is always ready for outputting transmission data. Therefore, a communication apparatus A that started transmission from a transmission terminal Tx1 at time t1 can start transmission upon a determination that no other communication apparatus started transmission because of a hardware time delay between transmitter and receiver until time t3, at which transmission data a of the communication apparatus A is inputted to the reception terminals RX1 and RX2 of each communication apparatus. Consequently, another communication apparatus B may start sending transmission data b from its transmission terminal Tx2 at time t2 which lies between time t1 and time t3.
If such a situation occurs, received data c at the reception terminals RX1 and RX2 of each communication apparatus becomes longer in H (High) level width than the transmission data by xcex94t1 as shown in FIGS. 14 and 15. As a result, the communication apparatus A and B each determine that each has received the transmission data different from that sent by each, accordingly, both communication apparatus stop sending the transmission data.
In order to resolve such a problem, the method disclosed in Japanese Patent Laid-open No. Hei 5-211511 controls the pulse width such that, as shown in FIG. 15, the falling of the transmission data a and b transmitted from the transmission terminals Tx1 and Tx2 takes place at point of time which has passed by xcex94xcex1 from time t3 at which the reception terminals RX1 and RX2 of the communication apparatus receive the transmission data a previously transmitted, xcex94xcex1 a being obtained by subtracting time xcex94t1 indicating a delay in reception of transmission data from time T corresponding to the bit information of digital data.
The above-mentioned conventional device is effective for so-called pulse width digital modulating (PWM scheme) in which, if the bit information of digital data is 0, the pulse width (namely, a H level time) is ⅔ of 1-bit time and, if the bit information is 1, the pulse width is ⅓ of the 1-bit time. However, in this PWM scheme, the bit information is PWM-controlled, thereby complicating the control of sending and receiving transmission data. On the other hand, in the bit serial scheme, in which, if the bit information of digital data is 0, the pulse width is 0, namely 1-bit time L (Low) level, and, if bit information 1, the pulse width is 1-bit time H (High) level, the pulse width of 1-bit information is not varied, thereby simplifying the control of sending and receiving transmission data. However, the technology disclosed in the above-mentioned patent laid-open corrects the data shift caused by a time lag between transmitter and receiver by varying the pulse width, so that this technique is not applicable to a bit serial scheme.
It is therefore an object of the present invention to provide a method of preventing data destruction in a multiplex communication system effectively in a bit serial scheme, which can prevent the destruction caused by collision of transmission data due to the time lag in the transmission data between the transmitter and the receiver.
In carrying out the invention and according to one aspect thereof, there is provided a method of preventing data destruction in a multiplex communication system in which a clock is provided for time-dividing the 1-bit data to perform bit serial communication control for establishing bit data depending on a state of a plurality of items of data in a central portion obtained by the time division. This method may be effected by carrying out the steps of starting, by the transmitter, after transmitting transmission data, a transmission clock when the transmission data has been received by the receiver; resetting, by the receiver, a reception clock when the received data has become nonpriority data; comparing the transmission data established by the transmission clock with the received data in a bit serial manner; and, stopping the transmission whenever a mismatch is found.
According to this novel configuration, the clocks of the transmitter and the receiver can be synchronized with each other. If there is a time delay of less than 1-bit time between the transmitter and the receiver, and two or more communication apparatuses start transmission during that time delay, data destruction due to data collision can be prevented.
In carrying out the present invention and according to another aspect thereof, a communication format to be transmitted by the transmitter has a non-prioritized bit signal after a unit address for determining transmission priority. According to this novel configuration, the number of communication apparatuses connected to the multiplex communication system can be increased.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.